PROJECT SUMMARY Detrimental health impacts of lead are largely attributed to long-term exposures to undetected lead, which are particularly troublesome and problematic because of the neurological damage to children, a situation that should not be tolerated by an advanced society like the U.S. The Flint Water Crisis and many other water catastrophes could have been avoided if early warning can be made possible through timely detection of lead in drinking water at the point of use. Our extensive customer interviews unambiguously suggest that current options for lead detection are unsatisfactory for on-site testing, as they represent two extremes: one being accurate but expensive, slow, and hard to use; and the other being low-cost, fast, and easy to use but inaccurate. NanoAffix Science LLC (NAFX) proposes to address the above unmet need and niche market product gap by empowering water users (particularly those in economically disadvantaged communities) and water service providers with a low-cost, easy-to-use, and accurate handheld tester for rapid detection of total lead in the tap water, right from the kitchen sink. The handheld lead tester combines a novel proprietary micro-sized sensor chip embedded in a proprietary test cell with a portable digital meter for direct readout of testing results. The Phase I project has successfully established the feasibility for detection of soluble lead in the tap water using an earlier version of the prototype handheld tester. The Phase II project will continue to develop the handheld tester toward total lead detection, better device uniformity, pilot scale-up manufacturing, and accurate calibration. At the end of the Phase II project, NAFX plans to produce 20 beta units of the handheld lead tester meeting all performance specifications for field validation by 10 initial customers (e.g., schools/daycares, end water users, and well water drillers). Major innovations of the proposed approach include accurate prediction of the particulate lead through partial digestion based on lead digestion kinetics, and strategic and synergistic improvement of the ultimate sensor prediction accuracy by (1) improving the physical sensor device uniformity (both intra-wafer and inter-wafer) through innovative device configuration and rigorous quality control; and (2) improving the calibration accuracy through innovative theoretical equilibrium chemistry modeling and machine learning data analytics. The NAFX handheld lead tester is the first of its kind to (1) offer all three features sought by customers: accurate, cheap, and fast; and (2) to simultaneously report all three types of lead: total lead (indicative of overall toxicity), soluble lead (indicative of slow leaching of lead), and particulate lead (indicative of sporadic flaking of lead), which thus can not only alert customers to the lead hazard in their drinking water but also enable customers to identify possible causes and most effective solutions to mitigate the lead contamination. Therefore, the project will result in not only considerable economic impact but also immense societal impact. The regular use of NAFX handheld tester - even if intermittently - will virtually eliminate the chance of chronic exposure to undetected lead, thereby accruing significant and predictable public health impact, especially in locations with the highest risk.